1. Field
The present disclosure generally relates to the fabrication of composite structures, and deals more particularly with a method and apparatus for fabricating concave and convex stiffeners such as stringers, especially those that are contoured.
2. Background
Composite laminate structural stiffeners are sometimes required to have complex contours tailored to particular applications. For example, in the aircraft industry, composite laminate stringers used to stiffen aircraft skins are sometimes contoured in one or more planes in order to match changes in the geometry of the skins.
Layup and forming of structural stiffeners with complex contours can be challenging because of the tendency of the uncured composite prepreg material to bridge or wrinkle in the areas of contours. Dry fabric cloth used to make fiber performs that are subsequently infused with resin may also wrinkle when formed to a desired preform shape having contours, particularly when tackified and/or multiple plies of the cloth are being formed to shape simultaneously. Bridging results in undesired resin rich-areas in the laminate, while wrinkling may produce undesired localized high stress concentrations. In order to minimize these problems, composite laminate structural stiffeners such as stringers are usually laid up by hand in order to minimize bridging and wrinkling. However, even using hand layup techniques, bridging and wrinkling of the laminate sometimes occurs which requires hand rework of the stiffener, typically using patches. Hand layup of stiffeners and rework of stiffener non-conformities is both labor-intensive and time-consuming, and therefore expensive.
Accordingly, there is a need for a method and apparatus for laying up and forming contoured composite stiffeners such as composite laminate prepreg stringers, that reduce non-conformities and touch labor. There is also a need for a method and apparatus of the type mentioned above which may increase production throughput while reducing factory floor space required for stiffener production.